This invention relates to tape handling, and in particular to the tape transports which are used in the audio magnetic tape industry for making copies of master tapes.
Typically a master tape in the order of 1000 feet in length is spliced end to end to form an endless loop of tape which is continuously driven past a magnetic read head for transferring audio information from the master tape in the master unit to blank tapes in one or more slave units. Tape handling devices of this nature are shown in U.S. Pat. Nos. 3,608,798 and 3,528,593. Precise control of the speed of the master tape past the read head is desired, and one drive system for the capstan drive at the read head is shown in U.S. Pat. No. 4,431,950. An improved construction for read and write heads is shown in U.S. Pat. No. 4,470,084, and a reel hub configuration used in feeding tapes into and out of the apparatus is shown in U.S. Pat. No. 4,432,506.
In a typical tape transport, the major portion of the master tape is stored in a loop bin, with tape being fed in at one end of the bin and removed from the other end of the bin for passing the capstan drives and read and/or write heads at the magnetic head station. The storage bins are used in both horizontal and vertical configurations, as shown in the aforementioned U.S. Pat. Nos. 3,608,798 and 3,528,593.
The maximum length of master tape which present day loop bins can handle is in the order of 1200 to 1800 feet, with the limitation being primarily due to the bulk of tape which needs to be contained in the bin. At the same time, there often is a need for capability to handle master tapes of substantially greater length. The aforementioned U.S. Pat. No. 3,528,593 proposes arranging a plurality of film feeding devices in edge to edge relation so that the length of tape stored can be increased, but gives no details of how this may be accomplished.
It has been determined that one cannot merely connect two or more of the endless loop tape bins in series for obtaining higher tape storage capacity because the smallest unbalances in the tape drive speeds in the various bins results in most of the tape concentrating in one bin with little or no tape in the other. This is a serious problem, since the master tape typically is operated continuously for many hours during a slave tape production operation. When the master tape is operated at high speed for many hours, very small differences in the dimensions of the drive components and the speed of the drive motors will produce major unbalances in tape storage conditions.
Accordingly, it is an object of the present invention to provide a new and improved control system for operating tape loop bins in series to maintain balance of the quantities of tape in each of the bins.
A further object is to provide such a control system including means for measuring the amount of tape in each bin, means for comparing the resultant measurements, and means for changing the drive speed for one of the bins to reduce the differences.
It is an additional object of the present invention to provide a control system for operating two magnetic tape loop bins in series, which control system can be utilized with the other controls of a tape loop bin for the necessary steps of loading the tape and unloading the tape, and also for use of the two bins independently when smaller master tapes are being copied. An additional object is provide such a control system which can be operated in conjunction with the conventional constant tape tension control systems.
Other objects, advantages, features and results will more fully appear in the course of the following description.